Devil May Cry 5 walkthrough/SM04

Location
On Mission 05: The Devil Sword Sparda, after destroying the Blood Cloth at the ship area, there will be a forced battle with one gas tank in the middle. After this battle, the player is supposed to destroy another Blood Cloth, instead, head towards the wall which has a yellow waste container nearby and spawn Nightmare, he will break this wall upon being called.

The location ahead has another forced battle, after all enemies are dealt with, search for a set of stairs in this area - this will lead V to the Secret Mission area.